Tractor Hauler fuel gauge electrical question

Actually its a 1953 chevrolet 1 ton flatbed. Factory 6v. but was on 12v. when I got it. (Will probably haul tractors when i am done though.)

I want to hook the 6v. gas gauge back up, but I need to know about how many amps it will probably draw. I know the current will go up and down with fuel level, but I need to be in the ballpark at least to get the voltage reducer installed right.

Thanks!
Kelvin

A 50 50 voltage divider (same resistance as sending unit) would reduce 12 down to 6 volts at the sender/load. Ive seen senders 0 to maybe 30 or 0 to maybe one hundred ohms. I think they make sold state voltage reducer clamps that would take 12 VDC in to 6 VDC out.

John T

There's NO reason to muck around with unregulated voltage drop resistors from the age of dinosaurs.

There's all sorts of solid-state regulators available from companies that cater to classic car enthusiasts.

Or, get a cheap generic DC power supply that plugs into a cigarette lighter and has a switch to set desired voltage from Wallaby World (or equivalent) and hard-wire it and tuck it out of sight under the dash somewhere. I have done exactly that a number of times. (A "6-Volt" system operated at about 7.4 Volts with the engine running.)

You can also build your own using an IC regulator for a couple of bucks. I've done that, as well, and still have a '53 GMC truck I set up that way.

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Basic converter showing how to tweak the voltage a bit as needed.

John T and Bob,

I just had to comment. Many people don't know or understand what is meant by a voltage divider. Its nice to see someone who does. Once had a legend in his own mind computer genius sit for three or more hours trying to rig up a joystick which is nothing more than one or two voltage dividers. Digital vs. analog. lol

There is a simple one amp three terminal by pass regulator LM7806 or equivalent type that will provide the necessary 6 volt output for your gauge. The only additional parts needed will be a couple of ceramic or mylar caps and possibly a silicon diode. I don't think your gauge draws nearly one amp, but you might need a heat sink as these do give out a little heat depending on load and higher amp versions and modifications are available. Radio Shack has them but they can be bought cheaper. Its just more convenient to buy them locally rather than buying them 10 or more at a time on line.

Google it and look at the images.

I agree with Bob a sold state voltage regulator is the best, I just had to throw out the voltage divider answer as one possible solution. However, in cases where you use a 6 volt coil on a 12 volt tractor the simple voltage dropping (12 down to 6) so called "Ballast Resistor" is pretty close to a 50 50 voltage divider where its resistance (say around 1.5 ohms) is close to the same as a 6 volt coil (say also around 1.5 ohms) give or take. On those fuel gauge senders, however, they are like 0 to 30 to 100 or so variable sliding ohms?? so a solid state constant 6 volt source would be my choice for accurate operation.

Love sparky chat,

John T too long retired EE and rusty as an old nail but still enjoy

Thanks for all the replies. I guess I should have clarified the situation.

The '53 chevy truck was already on 12v. when I bought it. I don't know and the previous owner did not know about the generator, whether it was changed to 12v. or not. He claims he never had problems with dead batteries but then he parked it in the early '90s.
I rewired it because a lot of the exposed wiring insulation was failing and I upgraded to more modern turn signals that did not require 2 bulbs at the rear of the truck at the same time on both sides like the original seemed to need.

About the only thing I have not got on 12v. is the fuel gauge. (The last guy just ignored it and kept plenty of fuel in the tank.)

Napa sold me a VT6187 voltage reducer. The instructions say to install 1 reducer for 1 amp draw at 6v. 2 for 2 amp draw, so forth up to 4 amps. Start putting them in series/ parallel to get current up to 8 amps.

I wanted to know ballpark amp draw on the 6v gauge, say at mid range/half full of the resistor in the tank, understanding the error in the gauge would multiply in both directions the farther the fuel level was from that point.

The service manual I got for the truck was not very helpful. It said to use GM part number xx fuel gauge tester to test the fuel gauge. A range of ohm readings for the sender would have been helpful.

Do you want to know how to get rich quick.
Take an L7806 6 volt regulator (currently available for $.30 each in quantities of ten) mount it on a stud heat sink and charge $12 for it. Of course you would have to sell several thousand -----. I wish I could sell some of my stuff with that kind of profit margin.
Do this with a lot of things and you are golden.

Meanwhile you farm and farm and hope you will at least break even if the weather and demand are good and the insects don't clean you out. Got to love it.